src/librustc_typeck/check/callee.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use super::autoderef;
  12 use super::check_argument_types;
  13 use super::check_expr;
  14 use super::check_method_argument_types;
  15 use super::demand;
  16 use super::DeferredCallResolution;
  17 use super::err_args;
  18 use super::Expectation;
  19 use super::expected_types_for_fn_args;
  20 use super::FnCtxt;
  21 use super::method;
  22 use super::structurally_resolved_type;
  23 use super::TupleArgumentsFlag;
  24 use super::UnresolvedTypeAction;
  25 use super::write_call;
  26
  27 use CrateCtxt;
  28 use metadata::cstore::LOCAL_CRATE;
  29 use middle::def_id::DefId;
  30 use middle::infer;
  31 use middle::ty::{self, LvaluePreference, Ty};
  32 use syntax::codemap::Span;
  33 use syntax::parse::token;
  34 use syntax::ptr::P;
  35
  36 use rustc_front::hir;
  37
  38 /// Check that it is legal to call methods of the trait corresponding
  39 /// to `trait_id` (this only cares about the trait, not the specific
  40 /// method that is called)
  41 pub fn check_legal_trait_for_method_call(ccx: &CrateCtxt, span: Span, trait_id: DefId) {
  42     let tcx = ccx.tcx;
  43     let did = Some(trait_id);
  44     let li = &tcx.lang_items;
  45
  46     if did == li.drop_trait() {
  47         span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
  48     } else if !tcx.sess.features.borrow().unboxed_closures {
  49         // the #[feature(unboxed_closures)] feature isn't
  50         // activated so we need to enforce the closure
  51         // restrictions.
  52
  53         let method = if did == li.fn_trait() {
  54             "call"
  55         } else if did == li.fn_mut_trait() {
  56             "call_mut"
  57         } else if did == li.fn_once_trait() {
  58             "call_once"
  59         } else {
  60             return // not a closure method, everything is OK.
  61         };
  62
  63         span_err!(tcx.sess, span, E0174,
  64                   "explicit use of unboxed closure method `{}` is experimental",
  65                   method);
  66         fileline_help!(tcx.sess, span,
  67                    "add `#![feature(unboxed_closures)]` to the crate attributes to enable");
  68     }
  69 }
  70
  71 pub fn check_call<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
  72                             call_expr: &'tcx hir::Expr,
  73                             callee_expr: &'tcx hir::Expr,
  74                             arg_exprs: &'tcx [P<hir::Expr>],
  75                             expected: Expectation<'tcx>)
  76 {
  77     check_expr(fcx, callee_expr);
  78     let original_callee_ty = fcx.expr_ty(callee_expr);
  79     let (callee_ty, _, result) =
  80         autoderef(fcx,
  81                   callee_expr.span,
  82                   original_callee_ty,
  83                   Some(callee_expr),
  84                   UnresolvedTypeAction::Error,
  85                   LvaluePreference::NoPreference,
  86                   |adj_ty, idx| {
  87                       try_overloaded_call_step(fcx, call_expr, callee_expr, adj_ty, idx)
  88                   });
  89
  90     match result {
  91         None => {
  92             // this will report an error since original_callee_ty is not a fn
  93             confirm_builtin_call(fcx, call_expr, original_callee_ty, arg_exprs, expected);
  94         }
  95
  96         Some(CallStep::Builtin) => {
  97             confirm_builtin_call(fcx, call_expr, callee_ty, arg_exprs, expected);
  98         }
  99
 100         Some(CallStep::DeferredClosure(fn_sig)) => {
 101             confirm_deferred_closure_call(fcx, call_expr, arg_exprs, expected, fn_sig);
 102         }
 103
 104         Some(CallStep::Overloaded(method_callee)) => {
 105             confirm_overloaded_call(fcx, call_expr, callee_expr,
 106                                     arg_exprs, expected, method_callee);
 107         }
 108     }
 109 }
 110
 111 enum CallStep<'tcx> {
 112     Builtin,
 113     DeferredClosure(ty::FnSig<'tcx>),
 114     Overloaded(ty::MethodCallee<'tcx>)
 115 }
 116
 117 fn try_overloaded_call_step<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 118                                       call_expr: &'tcx hir::Expr,
 119                                       callee_expr: &'tcx hir::Expr,
 120                                       adjusted_ty: Ty<'tcx>,
 121                                       autoderefs: usize)
 122                                       -> Option<CallStep<'tcx>>
 123 {
 124     debug!("try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?}, autoderefs={})",
 125            call_expr,
 126            adjusted_ty,
 127            autoderefs);
 128
 129     // If the callee is a bare function or a closure, then we're all set.
 130     match structurally_resolved_type(fcx, callee_expr.span, adjusted_ty).sty {
 131         ty::TyBareFn(..) => {
 132             fcx.write_autoderef_adjustment(callee_expr.id, autoderefs);
 133             return Some(CallStep::Builtin);
 134         }
 135
 136         ty::TyClosure(def_id, ref substs) => {
 137             assert_eq!(def_id.krate, LOCAL_CRATE);
 138
 139             // Check whether this is a call to a closure where we
 140             // haven't yet decided on whether the closure is fn vs
 141             // fnmut vs fnonce. If so, we have to defer further processing.
 142             if fcx.infcx().closure_kind(def_id).is_none() {
 143                 let closure_ty =
 144                     fcx.infcx().closure_type(def_id, substs);
 145                 let fn_sig =
 146                     fcx.infcx().replace_late_bound_regions_with_fresh_var(call_expr.span,
 147                                                                           infer::FnCall,
 148                                                                           &closure_ty.sig).0;
 149                 fcx.record_deferred_call_resolution(def_id, Box::new(CallResolution {
 150                     call_expr: call_expr,
 151                     callee_expr: callee_expr,
 152                     adjusted_ty: adjusted_ty,
 153                     autoderefs: autoderefs,
 154                     fn_sig: fn_sig.clone(),
 155                     closure_def_id: def_id
 156                 }));
 157                 return Some(CallStep::DeferredClosure(fn_sig));
 158             }
 159         }
 160
 161         // Hack: we know that there are traits implementing Fn for &F
 162         // where F:Fn and so forth. In the particular case of types
 163         // like `x: &mut FnMut()`, if there is a call `x()`, we would
 164         // normally translate to `FnMut::call_mut(&mut x, ())`, but
 165         // that winds up requiring `mut x: &mut FnMut()`. A little
 166         // over the top. The simplest fix by far is to just ignore
 167         // this case and deref again, so we wind up with
 168         // `FnMut::call_mut(&mut *x, ())`.
 169         ty::TyRef(..) if autoderefs == 0 => {
 170             return None;
 171         }
 172
 173         _ => {}
 174     }
 175
 176     try_overloaded_call_traits(fcx, call_expr, callee_expr, adjusted_ty, autoderefs)
 177         .map(|method_callee| CallStep::Overloaded(method_callee))
 178 }
 179
 180 fn try_overloaded_call_traits<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 181                                        call_expr: &hir::Expr,
 182                                        callee_expr: &hir::Expr,
 183                                        adjusted_ty: Ty<'tcx>,
 184                                        autoderefs: usize)
 185                                        -> Option<ty::MethodCallee<'tcx>>
 186 {
 187     // Try the options that are least restrictive on the caller first.
 188     for &(opt_trait_def_id, method_name) in &[
 189         (fcx.tcx().lang_items.fn_trait(), token::intern("call")),
 190         (fcx.tcx().lang_items.fn_mut_trait(), token::intern("call_mut")),
 191         (fcx.tcx().lang_items.fn_once_trait(), token::intern("call_once")),
 192     ] {
 193         let trait_def_id = match opt_trait_def_id {
 194             Some(def_id) => def_id,
 195             None => continue,
 196         };
 197
 198         match method::lookup_in_trait_adjusted(fcx,
 199                                                call_expr.span,
 200                                                Some(&*callee_expr),
 201                                                method_name,
 202                                                trait_def_id,
 203                                                autoderefs,
 204                                                false,
 205                                                adjusted_ty,
 206                                                None) {
 207             None => continue,
 208             Some(method_callee) => {
 209                 return Some(method_callee);
 210             }
 211         }
 212     }
 213
 214     None
 215 }
 216
 217 fn confirm_builtin_call<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
 218                                  call_expr: &hir::Expr,
 219                                  callee_ty: Ty<'tcx>,
 220                                  arg_exprs: &'tcx [P<hir::Expr>],
 221                                  expected: Expectation<'tcx>)
 222 {
 223     let error_fn_sig;
 224
 225     let fn_sig = match callee_ty.sty {
 226         ty::TyBareFn(_, &ty::BareFnTy {ref sig, ..}) => {
 227             sig
 228         }
 229         _ => {
 230             fcx.type_error_message(call_expr.span, |actual| {
 231                 format!("expected function, found `{}`", actual)
 232             }, callee_ty, None);
 233
 234             // This is the "default" function signature, used in case of error.
 235             // In that case, we check each argument against "error" in order to
 236             // set up all the node type bindings.
 237             error_fn_sig = ty::Binder(ty::FnSig {
 238                 inputs: err_args(fcx.tcx(), arg_exprs.len()),
 239                 output: ty::FnConverging(fcx.tcx().types.err),
 240                 variadic: false
 241             });
 242
 243             &error_fn_sig
 244         }
 245     };
 246
 247     // Replace any late-bound regions that appear in the function
 248     // signature with region variables. We also have to
 249     // renormalize the associated types at this point, since they
 250     // previously appeared within a `Binder<>` and hence would not
 251     // have been normalized before.
 252     let fn_sig =
 253         fcx.infcx().replace_late_bound_regions_with_fresh_var(call_expr.span,
 254                                                               infer::FnCall,
 255                                                               fn_sig).0;
 256     let fn_sig =
 257         fcx.normalize_associated_types_in(call_expr.span, &fn_sig);
 258
 259     // Call the generic checker.
 260     let expected_arg_tys = expected_types_for_fn_args(fcx,
 261                                                       call_expr.span,
 262                                                       expected,
 263                                                       fn_sig.output,
 264                                                       &fn_sig.inputs);
 265     check_argument_types(fcx,
 266                          call_expr.span,
 267                          &fn_sig.inputs,
 268                          &expected_arg_tys[..],
 269                          arg_exprs,
 270                          fn_sig.variadic,
 271                          TupleArgumentsFlag::DontTupleArguments);
 272
 273     write_call(fcx, call_expr, fn_sig.output);
 274 }
 275
 276 fn confirm_deferred_closure_call<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
 277                                           call_expr: &hir::Expr,
 278                                           arg_exprs: &'tcx [P<hir::Expr>],
 279                                           expected: Expectation<'tcx>,
 280                                           fn_sig: ty::FnSig<'tcx>)
 281 {
 282     // `fn_sig` is the *signature* of the cosure being called. We
 283     // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 284     // do know the types expected for each argument and the return
 285     // type.
 286
 287     let expected_arg_tys =
 288         expected_types_for_fn_args(fcx,
 289                                    call_expr.span,
 290                                    expected,
 291                                    fn_sig.output.clone(),
 292                                    &*fn_sig.inputs);
 293
 294     check_argument_types(fcx,
 295                          call_expr.span,
 296                          &*fn_sig.inputs,
 297                          &*expected_arg_tys,
 298                          arg_exprs,
 299                          fn_sig.variadic,
 300                          TupleArgumentsFlag::TupleArguments);
 301
 302     write_call(fcx, call_expr, fn_sig.output);
 303 }
 304
 305 fn confirm_overloaded_call<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 306                                     call_expr: &hir::Expr,
 307                                     callee_expr: &'tcx hir::Expr,
 308                                     arg_exprs: &'tcx [P<hir::Expr>],
 309                                     expected: Expectation<'tcx>,
 310                                     method_callee: ty::MethodCallee<'tcx>)
 311 {
 312     let output_type =
 313         check_method_argument_types(fcx,
 314                                     call_expr.span,
 315                                     method_callee.ty,
 316                                     callee_expr,
 317                                     arg_exprs,
 318                                     TupleArgumentsFlag::TupleArguments,
 319                                     expected);
 320     write_call(fcx, call_expr, output_type);
 321
 322     write_overloaded_call_method_map(fcx, call_expr, method_callee);
 323 }
 324
 325 fn write_overloaded_call_method_map<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 326                                              call_expr: &hir::Expr,
 327                                              method_callee: ty::MethodCallee<'tcx>) {
 328     let method_call = ty::MethodCall::expr(call_expr.id);
 329     fcx.inh.tables.borrow_mut().method_map.insert(method_call, method_callee);
 330 }
 331
 332 #[derive(Debug)]
 333 struct CallResolution<'tcx> {
 334     call_expr: &'tcx hir::Expr,
 335     callee_expr: &'tcx hir::Expr,
 336     adjusted_ty: Ty<'tcx>,
 337     autoderefs: usize,
 338     fn_sig: ty::FnSig<'tcx>,
 339     closure_def_id: DefId,
 340 }
 341
 342 impl<'tcx> DeferredCallResolution<'tcx> for CallResolution<'tcx> {
 343     fn resolve<'a>(&mut self, fcx: &FnCtxt<'a,'tcx>) {
 344         debug!("DeferredCallResolution::resolve() {:?}",
 345                self);
 346
 347         // we should not be invoked until the closure kind has been
 348         // determined by upvar inference
 349         assert!(fcx.infcx().closure_kind(self.closure_def_id).is_some());
 350
 351         // We may now know enough to figure out fn vs fnmut etc.
 352         match try_overloaded_call_traits(fcx, self.call_expr, self.callee_expr,
 353                                          self.adjusted_ty, self.autoderefs) {
 354             Some(method_callee) => {
 355                 // One problem is that when we get here, we are going
 356                 // to have a newly instantiated function signature
 357                 // from the call trait. This has to be reconciled with
 358                 // the older function signature we had before. In
 359                 // principle we *should* be able to fn_sigs(), but we
 360                 // can't because of the annoying need for a TypeTrace.
 361                 // (This always bites me, should find a way to
 362                 // refactor it.)
 363                 let method_sig = fcx.tcx().no_late_bound_regions(method_callee.ty.fn_sig())
 364                                           .unwrap();
 365
 366                 debug!("attempt_resolution: method_callee={:?}",
 367                        method_callee);
 368
 369                 for (&method_arg_ty, &self_arg_ty) in
 370                     method_sig.inputs[1..].iter().zip(&self.fn_sig.inputs)
 371                 {
 372                     demand::eqtype(fcx, self.call_expr.span, self_arg_ty, method_arg_ty);
 373                 }
 374
 375                 let nilty = fcx.tcx().mk_nil();
 376                 demand::eqtype(fcx,
 377                                self.call_expr.span,
 378                                method_sig.output.unwrap_or(nilty),
 379                                self.fn_sig.output.unwrap_or(nilty));
 380
 381                 write_overloaded_call_method_map(fcx, self.call_expr, method_callee);
 382             }
 383             None => {
 384                 fcx.tcx().sess.span_bug(
 385                     self.call_expr.span,
 386                     "failed to find an overloaded call trait for closure call");
 387             }
 388         }
 389     }
 390 }